Optical transmission systems, in particular optical fibre transmission systems, are widely used for sending signals over long distances. That is, electrical signals representing data are converted into optical signals, which are transmitted over the transmission medium (such as the optical fibre) to a receiver, where they are converted back to electrical signals. Signal detection processes are then performed in the receiver, in order to recreate as far as possible the data content of the original electrical signals. In order to achieve this recreation of the original data content, various signal detection techniques can be used, in order to compensate for the effects of distortion that occur in the transmission medium (such as the optical fibre).
It is known that linear distortion can be compensated to a large extent by adaptive linear equalizers, but there are also non-linear distortions, and it is more difficult to mitigate the effects of these. The document “Compensation of dispersion and nonlinear impairments using digital backpropagation”, E. Ip and J. Kahn, J. Lightwave Technol. 26,3416-3425 (2008), describes a technique whereby the received digitized signal is back-propagated toward the transmission end by solving, in the digital domain, the Non Linear Schrodinger equation that describes propagation in the optical fibre. This technique is computationally very demanding, and has not provided wholly satisfactory results.